The invention relates to a method for the catalytic treatment of exhaust gases of IC engines, and more particularly of engines used in vehicles, in which the exhaust gases continuously flow through a catalytic converter and also to an apparatus for performing the method.
When an IC engine is started from cold large amounts of noxious substances are emitted. Downstream catalytic converters call for a certain minimum temperature in order to become fully operational. Until this minimum temperature is reached the noxious substances are not converted and instead are discharged into the atmosphere.
Conventional three-way catalytic converters contain catalytic material for the oxidation of CO and unburnt hydrocarbons, and also material for the reduction of NO.sub.x. Owing to the delay in reaction in the catalytic converter before the operational temperature is reached more particularly CO and uburned hydrocarbons are involved, whereas there is no substantial emission of NO.sub.x until the normal operating temperature is reached.
In order reduce this delay in the reaction of the catalytic converter a large number of different possibilities have been investigated --at least theoretically--for instance the electrical heating of the exhaust gases prior to their entry into the catalytic converter, the additional heating of the catalytic converter or the keeping, heated up by thermal insulation or by the use of heat storage means.
In the case of the electrical heating of the exhaust gases or the catalytic converter very high amperages are required, which, if they are to be supplied by electrical generators installed in as a standard in motor vehicles, involve expensive development.
Keeping catalytic converters hot by thermal insulation or by thermal storage leads to the problem of overheating, especially when the system is running under full load conditions.